BMW 3 Series Glow Plug System Issues, Help Needed

Hi there! I had a pretty similar issue with my 2016 BMW 5 Series diesel last winter. I have some basic car knowledge but I'm no expert. The symptoms were exactly like yours, glow plug light staying on, rough cold starts, and that annoying smoke when accelerating. Took it to my workshop and it turned out to be a loose connection in the wiring to the preheater control unit. They found a damaged cable that wasn't making proper contact. The fix was relatively straightforward, they replaced the faulty wiring and connections. Cost me about 95 Euro and solved all those issues. Before jumping to conclusions about the preheating unit itself being bad, I'd suggest having them check the wiring and connections first, could save you some money. Could you share which engine variant you have in your 3 Series? Also, have you noticed if the symptoms get worse in any particular conditions (like really cold weather)? This info would help me tell you more about my experience.

Hey! I've got the same car and had identical symptoms at 122302 KM. Turned out my issue was actually the glow plug control module, not just the wiring. Had it diagnosed at my last service a few weeks ago. The weird thing was the smoke got way worse during cold weather. If you're seeing the same thick smoke and rough starts, I'd definitely get the control module checked out along with the wiring. In my case, replacing just the wiring didn't solve it, had to change the whole module to fix the preheating system properly. Let me know what you find out. Be sure to get a proper diagnosis before replacing parts, these diesels can be tricky with preheating issues!

Oh hey again! Thanks for sharing that info about your control module, that's really interesting and makes me think I should get mine checked again. You know what's funny? After my initial wiring fix last winter, the symptoms actually started creeping back about a month ago at around 125,000 KM. I'm getting that same thick smoke again, especially on cold mornings. Started thinking maybe that wiring fix was just a temporary solution. With what you've shared about your experience, I'm definitely going to have my mechanic take another look, specifically at the control module this time. You're spot on about these diesels being tricky, I probably should've dug deeper instead of just assuming the wiring fix would solve everything. Mind if I ask how much the control module replacement set you back? My mechanic's booked for next week, and I'd like to know what I might be in for cost-wise. Also, have you noticed any improvement in fuel consumption since getting it fixed? My fuel economy has been terrible lately, which I'm guessing might be related. Really appreciate you sharing your experience, seems like we're definitely dealing with the same issue here!

Hey there! Totally get what you're going through with those recurring symptoms. The control module replacement cost me around 450 for the part plus labor. Honestly, it was worth every penny, the car runs so much better now. And yes, my fuel consumption has improved quite a bit! I was burning through way more diesel before the fix. Just make sure your mechanic does a thorough diagnostic check before replacing anything. The symptoms can be really similar for different issues, as we both found out. Since you're booking next week, ask them to specifically check the control module resistance values, that's what confirmed the issue in my case. Hope this helps with your repair planning! Let me know how it goes at the mechanic's. Given the similar mileage and symptoms, I've got a feeling you're heading for the same fix I needed. Good luck with it!